1. Field of the Invention
The present invention relates to a window glass antenna to be attached to an automobile window glass panel for transmitting and receiving signals, such as mobile telephone signals, in an UHF band.
2. Description of the Prior Art
One conventional double-loop window glass antenna for use on an automobile window glass panel, for example, for transmitting and receiving signals, such as mobile telephone signals, in an UHF band, as disclosed in Japanese laid-open patent publication No. 4-14304 is shown in FIG. 1 of the accompanying drawings.
As shown in FIG. 1, the conventional double-loop window glass antenna, generally designated by the reference numeral 101, comprises two semicircular loop conductors 103a, 103b, two reactive conductors 104a, 104b connected respectively to the semicircular loop conductors 103a, 103b, and a ground conductor 105 connected to the reactive conductors 104a, 104b. These conductors 103a, 103b, 104a, 104b, 105 are mounted on a front or rear automobile window glass panel 102. The reactive conductors 104a, 104b are of an L shape interconnecting the ends of the semicircular loop conductors 103a, 103b and the ground conductor 105.
The junction between the semicircular loop conductors 103a, 103b is connected as a feed point 106 to the core 107a of a feed cable 107 whose outer conductor 107b is connected to the ground conductor 105. The double-loop window glass antenna 101 is thus supplied with electric energy from the feed cable 107 in an unbalanced configuration.
The conventional double-loop window glass antenna 101 is disadvantageous in that the antenna gain is lowered as the angle at which the window glass panel 102 is mounted on an automobile body, i.e., the angle between the horizontal plane and the window glass panel, is reduced. This is because the directivity pattern in a vertical plane of the double-loop window glass antenna 101 is relatively narrow. Therefore, the conventional double-loop window glass antenna 101 fails to provide sufficient antenna performance on those automobiles which have a front or rear glass panel inclined through a small angle for less aerodynamic resistance or design considerations.
Wide antenna patterns disposed on window glass panel surfaces or between laminated window glass layers for sufficient antenna performance are problematic for the following reasons:
Window glass panels for use on automobiles are bent into curved configurations to match automobile window frames. In a bending process, a flat window glass panel is placed on a mold, supplied into a heating furnace, and then bent while being heated up to a certain temperature. If such a flat window glass panel carries a wide antenna pattern and electrodes, the glass panel regions corresponding to the wide antenna pattern and electrodes have different temperatures than the other glass panel regions, with the results that the window glass panel may not be fully bent or may suffer local deformations. Therefore, window glass panels with wide antenna patterns may not be bent to a desired curved shape, or may produce distorted image reflections in local regions.